1. Field of the Invention
The present invention is in the field of method and apparatus for power-operation of a gate. More particularly, the present invention relates to a power-drive apparatus for moving a gate between opened and closed positions.
2. Related Technology
It is conventional to move gates, such as those which control access to a parking lot, to a gated community, or to private land, for example, by means of a power-drive unit which moves the gate between fully opened and fully closed positions. The gate may move horizontally along a guide way, may swing about a vertical hinge axis to open and close, or may be of "turn pike" barrier-gate type in which the barrier swings up through about 90.degree.. This latter type of barrier gate is commonly used in parking garages to control vehicle ingress and egress.
Ordinarily, the power-drive unit for such gates includes an electric motor with a speed reduction drive train coupled to the gate to effect its movement between the opened and closed positions. The limits of movement of the gate itself are generally set using conventional limit switches. Alternatively, the mechanism of the gate operator may be configured such that an approximate opened and closed position for the gate is set by the mechanical operation constraints of the mechanism itself. However, in each of these cases, the combined momentum of the drive motor, its speed reduction, and of the gate itself can result in the gate stopping short of its desired limit positions, or in overshooting the limit positions set by the limit switches or by the gate operating mechanism.
Thus, gate operators which rely upon limit switches alone to determine the limit positions of a gate are prone to apparently erratic changes in gate limit positions, and frequent complaints from owners that the gate operator is out of adjustment. One reason for this is because the gate operator and gate will be subject to differing levels of mechanical drag and friction during various operations, and will coast differing distances after the drive motor is shut off on various operations. Thus, the gate will coast to a position short of its desired fully opened or fully closed position, or will over-coast and strike a physical barrier in one of these positions.
In some cases, the amount of overshoot or coast of a gate beyond the limit position set by a limit switch can be sufficient that the gate either contacts a physical barrier, runs off the end of its guide way, or requires that a considerable overrun distance be provided for the gate in its guide way. In the former event, the gate and its gate operator power drive system are subjected to a severe impact, which can shorten their service lives. Additionally, the user of the gate will likely object to the jarring and noise such impact produces. In the latter event, the user will be quite unhappy with the gate operator mechanism because the gate will likely require manual restoration onto its guide way, and will probably be inoperative in an opened or closed position until this manual restoration of the gate is completed.
Some gate operators, in addition to the use of limit switches employ a braking device to physically stop movement of the gate and its associated drive motor and drive train when the desired limits of the gate's movement are reached. In other words, coasting of the gate is limited or eliminated in an attempt to set limit positions for the gate. The braking device is usually installed in the drive train of the gate operator, and may be actuated by the same limit switches which shut off the drive motor. In this case, a certain increment of added drive train shock and wear are attributable simply to the use of such a braking device. This is the case because in the moments before the brake is applied the drive train is involved in moving the gate in a certain direction (i.e., opening or closing the gate). However, immediately upon the brake being applied, the drive train is involved in decelerating and stopping the gate from moving in that certain direction. As a result, any slack or lost motion in the drive train it taken up quickly, and results in an impact or jarring in the drive train.
Moreover, the sudden reversal of forces caused within the drive train by the engagement of a braking device has the effects of imposing added strains on the components of the gate operator, increasing wear on the gate operator, and increasing its maintenance requirements. That is, in addition to the wear and tear of the drive train occasioned simply by driving the gate between its opened and closed positions, the drive train of a gate operator with a braking device is also subjected to a shock when braking is applied, and must endure the added wear and tear of being used to bring the gate to a halt at selected positions. Understandably, the heavier the gate is, and the more severe the shock of initial braking application and the more rapid the deceleration effected for the gate, the greater the adverse effect on the drive train of the gate operator will be.
Unfortunately, with many conventional gate operators, the only way to insure that the gate will stop at particular limit positions, and will not stop short of a fully opened or fully closed position, nor coast beyond these fully opened and fully closed positions to impact physical stops for the gate with undesired impact and noise, or to run off of a guide way, for example, is to use a definite (or immediate) and strong (as opposed to gradual and gentle) application of the braking device at particular limit positions. A shock in the drive mechanism for the gate inevitably results. Again and understandably, the heavier the gate moved by a gate operator and the greater its speed of movement (i.e., the greater the gate's momentum), the stronger the braking force required, and the greater the adverse effects of using the gate operator to brake movement of the gate. Further, the inclusion of a braking device in a gate operator undesirably increases the initial costs for the gate operator.
Another consideration with the so-called "barrier" gate operators is the lack of repeatability in the rest (i.e., gate closed) position for the gate arm with conventional operators. Such barrier gates are very common in parking garages, where they are used to control ingress and egress of motor vehicles from the garage. With these gate operators, the gate arm is carried by the gate operator itself, and is usually a length of wood or composite material weighing only a few pounds. However, in such a use the gate operator may experience a million operating cycles or more for each year of its service life, and may be expected to provide reliable service over several years of life. Thus, wear and tear of such a barrier gate operator is an important consideration.
Also, a barrier gate operator may cycle ever few seconds during intervals of heavy vehicle traffic, or may set for hours without cycling opened and closed during a weekend or evening, for example. Regardless of whether the recent service experience for the barrier gate operator has been one of frequent operations every few seconds, or one of a time interval of several hours since the last gate opening and closing cycle, the owners of such gate operators want the operation of the gate to be repeatable. That is, reliability of operation is very important, as is the appearance of operating crisply and with "military-like" precision. Moreover, owners of conventional barrier gate operators of this kind frequently object to the fact that the gate arm is stopped in a "droopy" position (i.e., below horizontal) on some occasions, and stops in a "half up" or slightly above horizontal position on other occasions.
Conventional gate operators are seen in U.S. Pat. Nos. 4,234,833; 4,429,264; 4,916,860;; 5,136,809; and 5,230,179. Of these conventional teachings, the '833 patent purports to include in an opening count of incremental movements of a gate that movement caused by coasting after the drive motor is shut off. Thus, this incremental coasting movement can be included also in the closing movement of the gate in order to insure that from its fully opened position the gate reaches its fully closed position. However, historical coasting of the gate after drive motor shut off is apparently not used in the art to predict gate coast during a current operation in order to stop the gate at a limit position.